Test Suite Heralds SGI's Growing Involvement with Linux

Testing Linux

August 13, 2000

By
Dennis E. Powell

A group of nearly 100 test tools
designed to make Linux kernel hacking easier is just one
manifestation of rapidly growing involvement in Linux by SGI.

The tools, announced on the linux
kernel mailing list, allow kernel developers to thoroughly test
changes before offering them up for incorporation into the kernel
source itself. The test suite announcement came just days ahead of
the opening of Linux World Expo, where SGI is expected to announce
additional contributions to Linux, demonstrate the world's largest
Linux display showing realtime rendering with a 128-chip cluster, and
announce new Linux graphical products and changes in SGI's policy
regarding use of its Open GL rendering technology.

The suite of 96 command-line test
applications--the number is growing--is not for users who simply
want to benchmark their systems. Instead, the goal is increased
stability of the Linux kernel.

"The idea is that the kernel
developers would have a copy of these tests that they would use as
tools, for system development," says Bill Roske, manager of
SGI's OS Test Development Group. "They make their changes,
incorporate them locally on their system, reboot the system, run
these tests, and have a better level of confidence that they haven't
broken anything else." The userspace benefit is indirect but,
Roske hopes, real.

"What users are going to be
getting, we hope, is a kernel that is much more stable, that has
benefited from the development community using tools like this."

While SGI will be maintainer of the
Linux Test Project, as it's called, Roske stressed that it is fully
Open Source and not SGI-driven.

"We have some preconceived ideas
of where we think it could go, but this is an Open Source project,
and as such we don't thoroughly control it," he said. "It
will go where the development community needs it to go.

"It's easy to run a few tests
from different virtual consoles, but when you get into running
hundreds or thousands of tests you need some sort of driver or
script. We have some of those in Irix and we're thinking about Open
Sourcing them, but we want to make sure that we're solving the
problems that the Linux development community is having. So that was
one of the reasons we are Open Sourcing the tests and got the message
out and will be having the box at Linux World, to start getting that
discussion going about what the community's needs are, and building
it up with the community rather than imposing a solution to a
problem."

The individual tests themselves are
fairly basic, notes Nathan Straz, a member of the LPT team at SGI.

"So far, 92 of the tests are
system-call tests that run one system call with a few parameters and
see if the tests work, then combine those to stress the kernel,"
he said. "They're very simple tests right now, but we have a lot
more to add in." And as it is, the tests can be reiterated and
combined to produce even more meaningful results.

"When you look at each
individually, they don't look like real difficult tests," said
Roske. "They're going through a valid path through the kernel,
and they'll verify that valid path. But what's going on under the
covers, especially on an SMP system, and we start getting into this
in scaling, is that when you start running multiple copies of the
same system call test or multiple different system call tests at the
same time, you start to stress some of the internal locking
capabilities of the kernel. Two things can happen there: one, you can
have a bottleneck within the kernel, where you'll slow down because
processes can't get past each other, or two, you have locking
heirarchy problems and the kernel starts unlocking things it didn't
have or locking things it's already got, and spinning out of control.
So it's functional testing as well as testing some of the more
stressed levels within the system."

Members of the LTP team will be at
Linux World Expo to discuss the project with kernel developers.